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    <title>Document</title>
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<body>
    <script>
        var num=[1,2,3,4,];
        var str=["wer","sdf","sjkdf"];
        console.log(num.concat(str));//arr1.concat(arr2,arr3)-----返回的是一个新的数组
        console.log(num.copyWithin(2,1));//arr.copyWithin(目标位置索引，开始复制的索引，结束的索引（可以不写-默认是arr.length）)
    </script>
</body>

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